Abstract
A polymer coating as polycaprolactone (PCL) is applied to improve the initial corrosion resistance of biodegradable magnesium. In addition, plasma electrolytic oxidation (PEO) is performed to increase adhesion between the polymer and the metal. However, when a complex-shaped material such as a screw is implanted in a bone, the surface coatings are locally damaged, and the protective role of the coating is not sufficiently maintained. In this study, the optimal conditions for producing a polymer coating on a screw were determined by varying the concentration of the PCL and the coating cycles, and were examined in vitro and in vivo. Among various the PCL coating conditions of 2∼6 cycles with 5∼7 wt.% concentrations, the 6 wt.% + 4 cycles group was applied uniformly to the screw thread. In the case of the non-uniform PCL layers, oxides and gases were present between the Mg and the PCL layer because internal magnesium corrosion and the layer peel off. The 6 wt.% + 4 cycles group had a high corrosion resistance due to the low wear on the thread. Denser and thicker bone formed around the PCL-coated screw in rat femur. This difference was due to the high corrosion resistance, which provided sufficient time for bone healing and promoting new bone growth.
Highlights
Biodegradable polymer coatings on magnesium (Mg) and its alloys improve the corrosion resistance of implants in the body over the long term and improves the biocompatibility of metallic Mg in biodegradable applications[1,2,3]
The PCL coating produced under the optimal conditions on a Mg plate was applied to the anodized magnesium screw, as described in a previous study, and we aimed to find the optimal number of cycles and concentration for producing uniform PCL layers on complex materials such as orthopaedic absorbent fixtures by examining the immersion of an artificial bone model plate in simulated body fluid and performing in vivo studies in a rat tibia
The surface of a magnesium screw was treated with Plasma electrolytic oxidation (PEO) to increase the surface area and hydrophilicity, thereby allowing a uniform and stable PCL layer to be formed
Summary
Biodegradable polymer coatings on magnesium (Mg) and its alloys improve the corrosion resistance of implants in the body over the long term and improves the biocompatibility of metallic Mg in biodegradable applications[1,2,3]. The important requirements for the coating to achieve the desired performance are uniformity, lack of porosity, biocompatibility and self-healing ability[4,5] Natural biodegradable polymers such as collagen, polysaccharides like chitosan, and synthetic biodegradable polymers such as polycaprolactone (PCL) and poly-L-lactide (PLLA) provide good protection and have exhibited biocompatibility on Mg6–8. It is difficult to achieve long-term corrosion protection using a thin biodegradable polymer coating, while an increase in the coating thickness could lead to cohesive failure To solve this problem, the biodegradable polymer consisting of monomers need an initiator such as hydroxyl groups for ring-opening polymerization[14,15]. There have been studies on forming polymer coatings on unusual shapes such as biodegradable scaffolds for improving the biocompatibility in the case of metallic magnesium[24], a non-uniform coating results in local corrosion. The PCL coating produced under the optimal conditions on a Mg plate was applied to the anodized magnesium screw, as described in a previous study, and we aimed to find the optimal number of cycles and concentration for producing uniform PCL layers on complex materials such as orthopaedic absorbent fixtures by examining the immersion of an artificial bone model plate in simulated body fluid and performing in vivo studies in a rat tibia
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